The goal of this project is to develop gene-based non-invasive imaging technology to visualize lentivirally infected cells and reservoirs in vivo longitudinally. The principle of our technology is engineering a replication-competent lentivirus, such as simian or feline immunodeficiency virus (SIV or FIV), with reporter genes in its genome, thus, each infected cell will express reporters delivered by the lentiviral infection and becomes detectable by in vivo imaging scanner, such as magnetic resonance spectroscopy/imaging (MRS/MRI), positron emission tomography (PET) and other technology. Based on our genetic engineering strategy, the expression of imaging reporter is independent from viral long terminal repeat (LTR) promoter, thus their expression is not limited by lentiviral latency/activation. The application of this in vivo imaging technology would allow us to identify the location of the infected cells and to visualize the dynamics of reservoirs in order to evaluate the effectiveness of highly active antiretroviral therapy (HAART) without killing the experimental animals, which is important for isolating lentiviral reservoirs for investigating the mechanisms involved in latency and reactivation of HIV. Our preliminary data have demonstrated the proof-of-principle that a replication-competent SIV encoding the MRI reporter can infect cells and express both green fluorescent protein (GFP) and the reporter in targeted cells. In Aim 1, we will examine the sensitivity of each reporter and imaging technology on rodent model infected with genetically engineered SIV. Before applying to much more expensive SIV/monkey model, in Aim 2, we will inoculate cats with the engineered FIV constructs as a pilot experiment to evaluate the imaging technology in vivo to reveal the locations of reservoirs along with host inflammatory reaction to lentiviral infection. Success of this project should enable us to apply the same in vivo imaging technology to investigate the persistence of simian immunodeficiency virus (SIV) in macaques and the efficacy of in vivo eradication strategies in the future.